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A curious incident during the course of an investigation into the explosion of a SpaceX rocket last month has raised the question of possible sabotage, adding a conspiratorial twist to the drama.

Rocket manufacturer SpaceX, a company that is trialling reusable rockets and has a plan to take humans to Mars, suffered a major setback on September 2 when one of its reusable Falcon 9 rockets exploded on a launch pad in Florida.

The company is owned by billionaire entrepreneur Elon Musk, and it seems he might be a little bit suspicious of one of one his main rivals, the United Launch Alliance.

Despite the recent objections from some US politicians, SpaceX is leading the investigation with help from the Air Force, NASA and the Federal Aviation Administration.

A week after the explosion Elon Musk implored the public to send in video and pictures of the explosion to help with the investigation. He said the company had not ruled out the potential of sabotage.

It might seem like a far-fetched idea but it's a conspiracy theory the company appears to have pursued, according to The Washington Post.

The paper reported a recent incident in which a SpaceX employee visited one of ULA's facilities at the Florida launch pad and asked to be given access to the roof of one of the company's buildings. According to sources familiar with the investigation, SpaceX officials had reportedly come across something suspicious they wanted to check out.

It's understood that SpaceX has images from a video that appear to show a strange shadow, then a white spot on the top of a building owned by ULA just over a kilometre away from the launch pad where the rocket exploded.

In the days following the explosion - which Musk called the most complex and difficult failure in the company's history - the SpaceX founder took to Twitter to highlight an area of inquiry in the investigation.

"Particularly trying to understand the quieter bang sound a few seconds before the fireball goes off," he wrote. "May come from rocket or something else."

The SpaceX employee who went to investigate the rooftop reportedly told ULA staff that the visit was not accusatory in nature but was ultimately denied access.

Instead, Air Force investigators were invited to survey the rooftop and were unable to find anything that pointed to a connection with the explosion.

SpaceX and ULA are heated rivals engaged in what The Washington Post described as "a long-running feud".

The two companies compete over contracts that are worth serious amounts of money each year.

Until Elon Musk decided he wanted to get into the rocket-making business and lead the charge to help humans become a multi planet species, ULA was dominant. The company previously held a monopoly on such contracts because it was the only launch provider certified by the Air Force.

However in 2014 SpaceX sued the US Air Force for the right to compete in a move that allowed the company to gain its official certification.

To give some insight into the adversarial nature of the relationship, in response to SpaceX gaining its certification ULA fired its CEO and hired someone who vowed to compete with Elon Musk's company.

Last week Elon Musk unveiled his long-awaited plan of how he intends to take potentially the first human convoy to Mars.

During his speech he took a moment to address the investigation and said getting to the bottom of what caused the rocket to explode is the company's "absolute top priority."

"We've eliminated all of the obvious possibilities for what occurred there," he said. "So what remains are the less probable answers."

He did not elaborate on what they might be.

Neither SpaceX or United Launch Alliance are commenting on the investigation.